The present invention relates to a microwave probe and particularly to a dielectric resonator probe for measuring surface resistance of a test material.
Design and construction of microwave devices requires knowledge of the microwave properties of materials used to construct the device. In the past, a dielectric post resonator has been used to measure room temperature permittivity and permeability of microwave insulators, as described in Marian W. Pospieszalski "On the Theory and Application of Dielectric Post Resonator" IEEE Transactions on Microwave Theory and Techniques, Pages 228-231, March, 1977, incorporated herein by reference. A dielectric rod resonator has also been used to obtain the value of the loss tangent of a material as described in Y. Kobayashi, et al, "Microwave Measurement of Dielectric Properties of Low-Loss Materials by the Dielectric Rod Resonator Method", IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-33, No. 7, Pages 586-592, July, 1985.
One of the material characteristics of interest is surface resistance. Previous devices for measuring surface resistance have included resonant cavity devices at millimeter wavelengths as described in F. J. Tischer, et al, "Resonant Cavities for the Measurement of the Surface Resistance of Conductors at Millimeter Wavelengths", Review of Scientific Instruments, Vol. 46, No. 1, Pages 11-14, January, 1975, incorporated herein by reference.
Previous microwave devices, although usable to provide certain measurements, have been relatively insensitive to small differences in surface resistance. Previous devices have also been difficult to use because of lack of satisfactory mode separation. Furthermore, many previous devices have required a relatively large sample size to make measurements at lower microwave frequencies where measurement accuracy is greatest.
Of particular interest are methods for determining surface resistance of high critical temperature (T.sub.c) superconducting materials. The previous uses of the dielectric post resonator have concentrated on room temperature measurements. Previous devices have not been easily adaptable to operation in cryogenic temperatures such as about 98.degree. K. or less. Measurement apparatus which has been used at low temperatures includes a discresonator apparatus. Such a disc resonator requires special processing of the sample to be tested, such as patterning of the disc. In most cases, the sample preparation destroys the usefulness of the sample for subsequent applications.